Forensic science-solutions-conductivity and pH

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A large proportion of the molecules of a strong acid will react with water molecules to produce H₃O⁺ ions. A large number of ions exist in the solution which ultimately results in greater conductivity.

Increasing the concentration of a weak acid in solution does not result in a greater proportion of acid molecules reacting with water molecules. Since a certain percentage of the weak acid molecules will dissociate having a greater number of weak acid molecules present will result in more ions in then solution, although the percentage ionised will remain the same. More ions will result in greater conductivity.

Identifying solutions

Several solutions of known substances were tested for conductivity and pH. The conductivity of a solution is the measure of how easily an electric current is conducted through the solution. Complete the table below. Click on the test button to see the test for each substance.
The concentration of each solution was the same.

Substance	Test	Conductivity	pH
Hydrochloric acid	Test
Sulfuric acid	Test
Citric acid	Test
Carbonic acid	Test
Caustic soda	Test
Ammonia	Test
Sugar	Test
Salt	Test

Hydrochloric and sulfuric are strong acids while citric and carbonic are weak acids. What can you conclude about the conductivity of weak and strong acids?

Would a concentrated solution of carbonic acid give a higher conductivity than a dilute solution of carbonic acid?

Solution

Ammonia acts as a base and reacts with water according to the equation below.
NH₃ + H₂O => OH^- + NH₄⁺
Look at the conductivity of the ammonia solution above. What can you say about the strength of ammonia as a base?

Four solutions of sugar, sulfuric acid, salt and ammonia were created and labeled "A", "B", "C" and "D". In an attempt to identify the solutions tests on pH and conductivity were carried out on each solution. Click to see the tests and complete the table below..

Jar	Substance	pH	Conductivity
A		9.9
B		7.0
C		1.0
D		7.0

When dissolving, some substances create negative and positive particles in the water. The more of these charged particles that are created the greater the conductivity of the solution.

Salt and sugar can not be classified as acid or base. Explain why salt has a greater conductivity than sugar. View the video on the right to see a tiny salt crystal dissolving in water.
What can you say about strong acids and strong bases as they dissolve in the water? Look at the conductivity of these substances.

Sourced from https://www.youtube.com/watch?v=9aYLonML69w 25/06/20 10.30 am